Composite metal conductor sealed to glass



COMPOSITE METAL CONDUCTOR SEALED T0 GLASS Filed May 18. 1967 .050 70 J25 I CH [B20250 .00/9 TO .0062 INCH 1 Inventor: Rober' t E. Lamb b (aw/7 5 His A tt TTES United States Patent 3,475,144 COMPOSITE METAL CONDUCTOR SEALED TO GLASS Robert E. Lamb, Willoughby, Ohio, assignor to General Electric Company, a corporation of New York Filed May 18, 1967, Ser. No. 639,582 Int. Cl. C03c 27/02 US. Cl. 29-195 6 Claims ABSTRACT OF THE DISCLOSURE A copper sheathed nickel, cobalt, iron alloy core wire conductor for sealing in outsized diameters to soft glass in glass-to-metal seals. The copper sheath constitutes 16% to 20% of the total weight of the wire and the core contains by weight not less than 38% nickel and not more than 6% cobalt.

BACKGROUND OF THE INVENTION Field of the invention Glass-to-metal seals of the type including a high expansion, low softening point glass and a copper sheathed nickel-iron alloy core wire known commercially as Dumet wire have been used for more than fifty years for electric incandescent lamps. Such seals are used extensively at present for electronic devices and the like as well as for electric lamps. Heretofore, the size of such wires in satisfactory seals of this type has been limited to a diameter not larger than 1 millimeter or 40 mils, a diameter of 0.8 millimeter or about 30 mils being regarded generally as the maximum. Usually the wire is not larger than 0.6 millimeter or about 25 mils in diameter because with wires of larger diameter disruptive stresses are apt to occur in the seal under normal operating conditions of the electrical device including the seal.

Description of the prior art The book Glass-to-Metal Seals by J. H. Partridge, published 1949 by The Society of Glass Technology, Sheflield, England, describes on pages 11 and 12 seals for electric lamps including wire consisting of a central core of 43% nickel-iron alloy coated with about 30% of its weight of copper electro-deposited on the core. Wires of the small diameter sizes given above are mentioned by Partridge in this passage and in United States Patent No. 2,524,263- Kingston, filed Mar. 4, 1944, patented Oct. 3, 1950, for the fabrication of glass-to-metal seals of the type described above. According to the table on page 8 of Partridge, such a wire may be made with a coeflicient of expansion in the longitudinal direction of 7.8)( and in the radial direction of 9.0 l0- cm./cm./C. for successful sealing to glasses having a coeflicient of expansion of about 9.0)(10 cm./cm./C.

In the United States Patent No. 1,498,908Fink, filed Jan. 23, 1915, patented June 24, 1924, a composite wire useful in seals of this type is disclosed which includes 53 to 55% iron, from 44 to 46% nickel, and from 0.75 to 1.25% manganese. In addition, the Pink alloy contains trace amounts of carbon, phosphorus, silicon and sulfur. A specific composition disclosed by Fink has a core of this nickel-iron alloy containing about 44% nickel and a copper sheath of which the thickness expressed in percent of the diameter of the core is approximately 6%, the approximate percentage of copper being about by volume of the total volume of the wire.

The Scott Patent No. 1,872,354, filed Feb. 8, 1930, patented Aug. 16, 1932, discloses a composite wire conductor having an outer sheath of copper and an inner core composed of an alloy containing iron, nickel and cobalt. A conductor said to be suitable for sealing to soft glass consists of an alloy core containing to 34% nickel,

4% to 17% cobalt, O to 1% manganese and the remainder iron and minor impurities and the outer copper sheath is maintained between 10% and 40% of the cross-sectional area of the conductor. The Scott patent is silent as to the diameter of the composite wire which is suitable for sealing to soft glass. Since the Scott composite wire is intended to replace the prior composite wire of the Fink patent, for example, having nickel-iron alloy cores, it is obvious that Scott contemplates wire diameters not larger than 0.8 mm. which, according to Partridge, is the maximum diameter for successful sealing wires of the Pink type to soft glass.

As far as applicant is aware no composite wire of the type disclosed by Scott has been commercially available heretofore apparently because it does not provide new or enhanced qualities of utility over prior wires of Fink, for example, to the extent which would justify its commercial production.

The limitations in diameter sizes of prior composite wires of the above type have been due to the inflection points of the materials making up the seal not being at the same temperature. The inflection point is the temperature at which there is an abrupt change in the rate of thermal expansion of the material. This has caused disruptive stresses in the seal with wire diameter sizes larger than 40 mils at temperatures met in practical use of such seals.

SUMMARY OF THE INVENTION The present invention is based on the discovery that composite wires of the above type in diameter sizes of 50 mils up to and including 125 mils may be sealed to soft glass having a coefficient of expansion of approximately l0 when the copper sheath constitutes 16% to 20% of the total weight of the wire and the core contains by weight not less than 38% nickel, not more than 6% cobalt, manganese in a small but effective amount up to 1.25 balance essentially iron.

The principal object of the invention is to provide a composite leading-in wire of the above type useful in glass-to-rnetal seals in sizes of 50 mils up to and including mils in diameter and a glass-to-metal seal including such wire.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing a composite wire is shown in a fragmentary, side elevational view, partly in section, with legends applied thereto suitable for illustrating the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite wire of the present invention has a copper sheath covering a nickel-cobalt-iron alloy core. The core includes by weight 38% to 46% nickel, 4% to 6% cobalt, 0.25% to 1.25% manganese, balance primarily iron. The copper of the sheath is oxygen free and constitutes 16% to 20%, inclusive, of the total weight of the composite wire.

With a diameter size of 50 mils and a copper sheath constituting 16% of the total weight of the wire, the thickness of the sheath is 1.9 mils. When the copper sheath constitutes 20% of the total weight of this size wire the thickness of the sheath is 2.5 mils. A copper sheath constituting 16% of the total weight of a composite wire of 125 mils diameter is 4.8 mils thick and a copper sheath constituting 20% of the total weight of a 125 mil diameter wire is 6.2 mils.

The addition of cobalt in amount not more than 6% by weight to the nickel-iron alloy of the core wherein the nickel is present in amount greater than 36% by weight raises the temperature of the inflection point of the core, that is the temperature at which there is an abrupt change in the rate of linear thermal expansion of the core. For example, the inflection point of an alloy consisting of 41.10% nickel, 4.83% cobalt, 0.29% manganese, balance essentially iron, is at a temperature of about 450 C., whereas the inflection point of an alloy consisting of 41.52% nickel, 0.52% manganese, balance essentially iron, is about 365 C. The linear coeflicient of expansion of the above cobalt-containing core of the present invention is approximately 70 10-' cm./cm./ C. between room temperature (20 C.) and 450 C. The linear coeflicient of expansion of the above core material free from cobalt is approximately 53 10 cm./cm./ C. between room temperature and its inflection temperature of 365 C.

A type of glass in extensive use for sealing to Dumet type wires is a glass having a high lead content, a coefficient of expansion in the temperature range of to 300 C. of about 89 to 91x10, an annealing point in the range of 428 C. to 435 C., approximately, and a strain point or lower annealing temperature in the range of 395 C. to 404 C. A glass of this type known in the trade as G12 or 0120 glass has an annealing point of 433 C. and a strain point of 400 C.

In order to fabricate useful seals including this glass and Dumet wire the inflection point of the wire must be at least as high as the strain point of the glass. Preferably the inflection point of the wire is as high as or higher than the annealing point of the glass to avoid disruptive stresses in the completed seal. Dumet wire including the cobalt-containing core of the preceding paragraph satisfies this requirement whereas Dumet Wire including the cobalt-free core of the preceding paragraph does not satisfy this requirement. Wire including the cobalt-containing core provided with a copper sheath of suflicient weight in the range of 16% to 20% of the total weight of the wire to obtain a radial coefficient of expansion of 90x10 is useful in such seals whereas wire having a similar copper sheath on the cobalt-free core would not be useful for such seals.

A composite wire constituting the preferred embodiment of the invention has a nickel-cobalt-iron core consisting of 39% nickel, /2% cobalt, 1% manganese, balance essentially iron, and the copper sheath constitutes 18% by weight of the total weight of the composite wire. The preferred embodiment has a radial coeflicient of expansion of 90x10 and a longitudinal coeflicient of expansion of 70x10 cm./cm./ C. The electrical resistivity is 58 ohms per circular mil foot and the thermal conductivity about 17 cal./cm./sec./cm. C.

The composite wire constituting the preferred embodiment of the invention makes a satisfactory seal to 0120 glass in diameter sizes including 125 mils. The length of the seal is the limiting factor in the maximum diameter size that can be used as the axial expansion of the com- 4 posite wire is somewhat less than the radial expansion, as is usual in wires of this type. Composite Wires of the invention having a diameter of 125 mils are successfully sealed into 0120 glass when the length of the seal, that is, the length of the joint between the glass and the copper sheath is approximately 3 millimeters maximum. The length of the seal may be increased somewhat, when desired, with wires of smaller diameter.

The composite wire of the present invention may be made by conventional techniques comprising, in brief, inserting the core in the form of a bar or rod into a copper sleeve with a thin sheet of brass interposed between the sleeve and the core, brazing in dry hydrogen at a temperature slightly above the melting point of brass but well below that of copper and that of the core and then swaging and cold-drawing the brazed bar to the desired wire diameter.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A composite leading-in conductor having high electrical and heat conductivity consisting essentially of a core of nickel-cobalt-iron alloy and a copper sheath brazed to said core, sadi core comprising by weight 38% to 46% nickel, 4% to 6% cobalt, manganese in small but effective amount up to 1.25%, balance essentially iron, said sheath being of oxygen free copper and constituting 16% to 20% of the total weight of the composite conductor, the inflection point of said conductor being higher than the annealing point of 0120 glass, the longitudinal coefficient of thermal expansion of said conductor from room temperature to the annealing point of said glass being about 10 cm./cm./ C. and the radial coeflicient of thermal expansion thereof being approximately x10- said conductor being hermetically sealable in diameters of 50 mils up to and including mils to soft glass having a coeflicient of thermal expansion of approximately 90X 10- for use in glass-to-metal seals.

2. A leading-in conductor according to claim 1 wherein the core consisting essentially of by weight 39% to 42% nickel, 4.5% to 6% cobalt, 0.75% to 1.25% manganese, balance essentially iron and the sheath constitutes 16% to 20% of the total weight of the conductor.

3. A leading-in conductor according to claim 1 wherein the core consisting essentially of by weight 41.10% nickel, 4.83% cobalt, 0.29% manganese, balance essentially iron and the sheath constitutes 16% to 20% of the total weight of the wire.

4. A leading-in conductor according to claim 1 wherein the core consisting essentially of by weight 39% nickel, 5.5% cobalt, 1.0% manganese, balance essentially iron and the sheath constitutes 18% of the total weight of the conductor.

5. A glass-to-Inetal seal comprising a high expansion, low softening point glass having a coefficient of expansion of about 89 to 91 10- and a strain point in the range of 395 C. to 404 C. and a composite leading-in conductor bonded to said glass, said conductor comprising a core of nickel-cobalt-iron alloy and an oxygen free copper sheath brazed to said core, said core consisting essentially of by weight 38% to 46% nickel, 4% to 6% cobalt, manganese in small but effective amount up to 1.25 balance essentially iron, said sheath constituting 16% to 20% of the total weight of the composite conductor, the inflection point of said conductor being higher than the strain point of said glass, the longitudinal coeflicient of expansion of said conductor from room temperature to the strain point of said glass being about 70 10- cm./cm./ C., and the radial coeflicient of expansion thereof being equal approximately to the coeflicient of expansion of said glass.

6. A glass-to-metal seal according to claim 5 characterized in that the core consists essentially of by weight 39% nickel, 5.5% cobalt, 1.0% manganese, balance essentially iron and the sheath constitutes 18% of the total weight of the conductor.

References Cited UNITED STATES PATENTS 1,794,983 3/ 1931 Ritter 29--196.3 1,872,354 8/1932 Scott 29183.5 2,524,263 8/1950 Kingston 29-1963 X 2,677,877 5/1954 Cox 29195.5 1,498,908 1/1915 Fink.

HYLAND BIZOT, Primary Examiner US. Cl. X.R. 

